The present invention relates to image reading apparatus that is applicable to facsimile apparatus, digital photocopier apparatus and the like, and more particularly to image reading apparatus that uses a contact type image sensor device to read a document.
FIG. 1 indicates a conventional image reading apparatus that uses a contact type image sensor.
In FIG. 1, a frame 4 has a mounting surface 4a that is one step below a surface 4b. An adhesive fixes a sensor base plate 2 of a contact type of full-size image sensor to the mounting surface 4a of this frame 4. A document 7 that is sent by conveyor system is pressed against the sensor base plate 2 by a rotating platen roller 1. Then, when the light from a light source passes through the light-receiving window 6 and is irradiated to the document 7, the contact type image sensor optically reads the document 7. In such an image reading apparatus, the width of the sensor base plate 2 is large and so the document 7 that is sent is surely fed between the platen roller 1 and the sensor base plate 2.
In addition, as shown in FIG. 2, an image reading apparatus is proposed, which has a gap 8 formed between the sensor base plate 2 and a side wall 4c between the surface 4b and the mounting surface 4c. In this case, the width of the sensor base plate 2 is relatively large and so the width of the gap 8 is small. Thus, the document that is sent from the direction indicated by the arrow (either a .DELTA. or a .largecircle.) first strikes the sensor base plate 2 or the platen roller 1 and is then fed to between the platen roller 1 and the sensor base plate 2. The document is then conveyed in a favorable manner.
Making the width of the sensor base plate 2 smaller has been proposed in order to make image reading apparatus more compact and lower in price. In this case, as shown in FIG. 3, the width of the gap 8 formed between the sensor base plate 2 and the frame 4 becomes larger. Thus, as indicated by the arrow marked with a .DELTA., the document that is sent along the surface 4b of the frame 4 enters between the platen roller 1 and the sensor plate 2 but a document that is sen from the direction indicated by the arrow marked with an X enters the gap 8 and therefore results in the frequent occurrence of paper jams.
In order to prevent paper jams such as this, it is possible to have, as indicated in FIG. 4, a reduced width for the gap 8 so that the contact edge portion (E) for the surface 4b of the frame 4 and the side wall 4c is made closer to the platen roller 1. However, in such a structure, a gap between the contact edge portion (E) and the platen roller 1 either practically disappears or contacts so that the document is caught between the contact edge portion (E) and the platen roller 1 so that an extra load is created when the document is conveyed. The presence of such a load also makes it more likely for a paper jam to occur.
Furthermore, it has been proposed (Japanese Publication No.31662-1890) to provide a pressure plate at a position in contact with a document feed roller and to have a document feed mechanism that scans the document in the vicinity of a distal end portion of this pressure plate. Also proposed (Japanese Patent Publication No.23794-1983) has been a scan and read mechanism in which the document is fed to between a rotating pressure rubber roller and a guide member that presses the rubber roller, so that the document will be always fed smoothly even if such mechanisms are used.